The invention relates to driving circuits, and in particular to methods for controlling driving circuits by switching.
FIG. 1 shows a conventional H-bridge driving circuit. FIG. 2 is waveform diagram of signals input to the conventional H-bridge driving circuit in FIG. 1. Referring to FIGS. 1 and 2, the H-bridge driving circuit has a driving unit having transistors Q1 and Q2 and an inverse driving unit having transistors Q3 and Q4. A pulse width modulation (PWM) signal generating unit (not shown in FIG. 1) generates signals S21 to S24 as shown in FIG. 2. The signals S21 and S24 turn on the driving unit, and the signals S22 and S23 turn off the inverse driving unit, so that a current I flows through an induction coil L according to the solid line in FIG. 1. The signals S22 and S23 are then changed to turn on the inverse driving unit, and the signals S21 and S24 are changed to turn off the driving unit, so that a current I flows through the induction coil L according to the dashed line in FIG. 1. An external motor rotor (not shown in FIG. 1) is thus drive continuously. As shown in FIG. 2, there is a time difference ΔT between the falling edges of the pulses on the signals S21 and S24 and the rising edges of the pulses on the signals S22 and S23.
Referring to FIG. 3, when the phases of the pulses on the signals S21 and S24 fall, the H-bridge driving circuit simultaneously generates a large induction current I′ to a capacitor C according to the solid line in FIG. 3, serving as a ripple current. The ripple current can generate high temperature, resulting in shortened lifetime of the capacitor C, especially for an electrolysis capacitor especially.